This invention relates to methods of producing transparent, fire resistant polycarbonate compositions and more particularly transparent, fire resistant polycarbonate compositions comprising flame retardant salts.
Plastics, and in particular polycarbonates, are increasingly being used to replace metals in a wide variety of applications, from car exteriors to aircraft interiors. The use of polycarbonate instead of metal decreases weight, improves sound dampening, and makes assembly of the device easier. Unfortunately, polycarbonates are inherently flammable, and thus require the addition of flame retardants. A variety of different materials have been used, some of which are set forth in U.S. Pat. Nos. 3,971, 4,028,297, 4,110,299, 4,130,530, 4,303,575, 4,335,038, 4,552,911, 4,916,194, 5,218,027, and 5,508,323. The challenge is to identify economical, environmentally friendly flame retardant additives that provide the requisite flame resistance, but without compromising desirable polycarbonate properties such as strength and clarity.
Flame resistance in polycarbonate compositions may be achieved using a sulfonic acid salt such as potassium perfluorobutane sulfonate (also known as xe2x80x9cRimar saltxe2x80x9d, or xe2x80x9cKPFBSxe2x80x9d) as disclosed, for example, in U.S. Pat. No. 3,775,367. While flame resistant, transparent polycarbonate compositions may be produced using KPFBS, optimum flame resistance is found for levels of salt that can result in haze, especially for thicker samples. The amount of flame retardant that can be added when an optically clear product is desired is thus limited. Addition of synergistic additives such as tetrabromobisphenol A to improve flame retardancy is not possible where xe2x80x9cECO-friendlyxe2x80x9d standard that prohibit the inclusion of bromine or chlorine are in place. Accordingly, there remains a need in the art for methods of producing polycarbonates that are not only highly flame resistant, but also transparent.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a method for reducing haze in fire resistant polycarbonate compositions, comprising
blending a flame retardant salt with a first polycarbonate to produce a concentrate; and,
blending the concentrate with a second polycarbonate to form a transparent, fire resistant polycarbonate composition.
It has surprisingly been found that highly flame resistant and transparent polycarbonate compositions may be obtained by blending a flame retardant salt with a first polycarbonate to produce a concentrate, then blending the concentrate with a second polycarbonate to form a transparent, fire resistant polycarbonate composition. The concentrate is preferably a pelletized blend of KPFBS and polycarbonate. In another preferred embodiment, the first polycarbonate and the second polycarbonate are the same.
Not wishing to be bound by any theory, it is believed that the present method of using the flame retardant salt-polycarbonate concentrate aids in completely dissolving the salt into the final polycarbonate composition by giving the salt crystals an additional heat history. The additional heat history may allow for effectively solubilizing greater amounts of salt into the matrix. The present method allows for the use of higher levels of flame retardant salt, thereby providing robust flame performance while at the same time maintaining polymer transparency.
Non-limiting examples of suitable sulfonic acid salts are perfluoroalkane sulfonate alkali metal, C1-C6 alkylammonium, or ammonium salts. Such salts are described in the above-mentioned U.S. Pat. No. 3,775,367, and include, for example, salts such as sodium, potassium, or tetraethyl ammonium perfluoromethylbutane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoromethane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoroethane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoropropane sulphonate; sodium, potassium, or tetraethyl ammonium perfluorohexane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoroheptane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoroctanesulphonate; sodium, potassium, or tetraethyl ammonium perfluorobutane sulfonate; and sodium, potassium, or tetraethyl ammonium diphenylsulfon-3-sulphonate; and mixtures comprising at least one of the foregoing salts. Potassium perfluorobutane sulfonate (KPFBS) and potassium diphenylsulfon-3-sulphonate (KSS) are particularly preferred.
The salt, and KPFBS in particular, is present in the final composition in quantities effective to achieve a flame resistance rating of UL94-V0 at 3.2 millimeters. Generally, effective amounts of flame retardant salt present in the final composition is about 0.01 to about 1.0, preferably about 0.05 to about 0.20, and most preferably about 0.06 to about 0.12, and even more preferably 0.08-0.10% by weight based upon the total weight of the resin in the final composition. To achieve these final concentrations, it is convenient to produce a concentrate wherein the amount of flame retardant salt in the concentrate is about 0.1 to about 5.0, preferably about 0.5 to about 2.0, and most preferably about 0.8 to about 1.2% by weight of the total amount of the concentrate.
The polycarbonate component may be made by interfacial processes or by catalytic transesterification, may be either branched or linear in structure, and may include functional substituents. As used herein, the terms xe2x80x9cpolycarbonatexe2x80x9d and xe2x80x9cpolycarbonate compositionxe2x80x9d includes compositions having structural units of the formula (I): 
in which at least about 60 percent of the total number of R1 groups are aromatic organic radicals and the balance thereof are aliphatic, alicyclic, or aromatic radicals. Preferably, R1 is an aromatic organic radical and, more preferably, a radical of the formula (II):
xe2x80x94A1xe2x80x94Y1xe2x80x94A2xe2x80x94xe2x80x83xe2x80x83(II) 
wherein each of A1 and A2 is a monocyclic divalent aryl radical and Y1 is a bridging radical having one or two atoms which separate A1 from A2. In an exemplary embodiment, one atom separates A1 from A2. Illustrative non-limiting examples of radicals of this type are xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94S(O)xe2x80x94, xe2x80x94S(O)2xe2x80x94, xe2x80x94C(O)xe2x80x94, methylene, cyclohexyl-methylene, 2-[2.2.1]-bicycloheptylidene, ethylidene, isopropylidene, neopentylidene, cyclohexylidene, cyclopentadecylidene, cyclododecylidene, and adamantylidene. The bridging radical Y1 can be a hydrocarbon group or a saturated hydrocarbon group such as methylene, cyclohexylidene or isopropylidene.
Polycarbonates can be produced by the interfacial reaction of dihydroxy compounds in which only one or two atoms separate A1 and A2. As used herein, the term xe2x80x9cdihydroxy compoundxe2x80x9d includes, for example, bisphenol compounds having general formula (III) as follows: 
wherein Ra and Rb each represent a monovalent hydrocarbon group and may be the same or different; p and q are each independently integers from 0 to 4; and Xa represents one of the groups of formula (IV): 
wherein Rc and Rd each independently represent a hydrogen atom or a monovalent linear or cyclic hydrocarbon group and Re is a divalent hydrocarbon group.
Some illustrative, non-limiting examples of suitable dihydroxy compounds include the dihydroxy-substituted aromatic hydrocarbons disclosed by name or formula (generic or specific) in U.S. Pat. No. 4,217,438, which is incorporated herein by reference. A nonexclusive list of specific examples of the types of bisphenol compounds that may be represented by formula (III) includes the following:
1,1-bis(4-hydroxyphenyl) methane;
1,1-bis(4-hydroxyphenyl) ethane;
2,2-bis(4-hydroxyphenyl) propane (hereinafter xe2x80x9cbisphenol Axe2x80x9d or xe2x80x9cBPAxe2x80x9d);
2,2-bis(4-hydroxyphenyl) butane;
2,2-bis(4-hydroxyphenyl) octane;
1,1-bis(4-hydroxyphenyl) propane;
1,1-bis(4-hydroxyphenyl) n-butane;
bis(4-hydroxyphenyl) phenylmethane;
2,2-bis(4-hydroxy-1-methylphenyl) propane;
1,1-bis(4-hydroxy-t-butylphenyl) propane;
2,2-bis(4-hydroxy-phenyl) propane;
1,1-bis(4-hydroxyphenyl) cyclopentane; and
1,1-bis(4-hydroxyphenyl) cyclohexane.
It is also possible to employ two or more different dihydric phenols or a copolymer of a dihydric phenol with a glycol or with a hydroxy- or acid-terminated polyester or with a dibasic acid or hydroxy acid in the event a carbonate copolymer rather than a homopolymer is desired for use. Polyarylates and polyester-carbonate resins or their blends can also be employed. Branched polycarbonates are also useful, as well as blends of linear polycarbonate and a branched polycarbonate. The branched polycarbonates may be prepared by adding a branching agent during polymerization.
These branching agents are well known and may comprise polyfunctional organic compounds containing at least three functional groups, which may be hydroxyl, carboxyl, carboxylic anhydride, and mixtures thereof. Specific examples include trimellitic acid, trimellitic anhydride, trimellitic trichloride, tris-p-hydroxy phenyl ethane, isatin-bis-phenol, tris-phenol TC (1,3,5-tris((p-hydroxyphenyl)isopropyl)benzene), tris-phenol PA (4(4(1,1-bis(p-hydroxyphenyl)-ethyl) alpha, alpha-dimethyl benzyl)phenol, trimesic acid and benzophenone tetracarboxylic acid. The branching agents may be added at a level of about 0.05-2.0 weight percent. Branching agents and procedures for making branched polycarbonates are described in U.S. Pat. Nos. 3,635,895 and 4,001,184, which are incorporated by reference. All types of polycarbonate end groups are contemplated as being within the scope of the present invention.
Preferred polycarbonates are based on bisphenol A, in which each of A1 and A2 is p-phenylene and Y1 is isopropylidene. Preferably, the average molecular weight of the polycarbonate is in the range of about 5,000 to about 100,000, more preferably in the range of about 10,000 to about 65,000, and most preferably in the range of about 15,000 to about 35,000. Furthermore the polycarbonate has a melt viscosity rate (MVR) of about 4 to about 30 cm3/10 min.
Additionally, the polycarbonate composition may include various additives ordinarily incorporated in resin compositions of this type. Such additives are, for example, fillers or reinforcing agents; heat stabilizers; antioxidants; light stabilizers; plasticizers; antistatic agents; mold releasing agents; additional resins; and blowing agents. Examples of fillers or reinforcing agents include glass fibers, asbestos, carbon fibers, silica, talc, and calcium carbonate. Examples of heat stabilizers include triphenyl phosphite, tris-(2,6-dimethylphenyl)phosphite, tris-(mixed mono-and di-nonylphenyl)phosphite, dimethylbenzene phosphonate, tris-(2,4-di-t-butylphenyl)phosphite, and trimethyl phosphate. Examples of antioxidants include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Examples of light stabilizers include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)-benzotriazole and 2-hydroxy-4-n-octoxy benzophenone. Examples of plasticizers include dioctyl-4,5-epoxy-hexahydrophthalate, tris-(octoxycarbonylethyl)isocyanurate, tristearin and epoxidized soybean oil. Examples of the antistatic agent include glycerol monostearate, sodium stearyl sulfonate, and sodium dodecylbenzenesulfonate. Examples of mold releasing agents include stearyl stearate, pentaerythritol tetrastearate, beeswax, montan wax and paraffin wax. Examples of other resins include but are not limited to polypropylene, polystyrene, polymethyl methacrylate, and polyphenylene oxide. Combinations of any of the foregoing additives may be used. Such additives may be mixed at a suitable time during the mixing of the components for forming the composition. A preferred time is during the blending of the concentrate and the second polycarbonate.
In particular, other flame retarding components may be present in the compositions, for example cyclic siloxanes, at levels effective to import improved fire-resistance properties. Suitable quantities will generally be in the range of about 0.01 to about 0.5 parts per hundred parts by weight of resin (phr), preferably about 0.02 to about 0.30 phr. Suitable cyclic siloxanes, which may be present, include those having the general formula (V) 
wherein n is 0-7 and each R is independently an alkyl group having from 1 to about 36 carbons, an alkoxy group having from 1 to about 36 carbons, a fluorinated or perfluorinated alkyl or alkoxy group having from 1 to about 36 carbons, an arylalkoxy group having from 7 to about 36 carbons, an aryl group having from 6 to about 14 carbons, an aryloxy group having from 6 to about 14 carbons, a fluorinated or perfluorinated aryl group having from 6 to about 14 carbons, and an alkylaryl group having from 7 to about 36 carbons. Specific examples of cyclic siloxanes include hut are not limited to octaphenylcyclotetrasiloxane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, trimethyltriphenylcyclotrisiloxane, and tetramethyltetraphenylcyclotetrasiloxane.
In the practice of the process, the flame retardant salt is blended with a first polycarbonate to form a concentrate that is an intimate blend. The concentrate is further blended with a second polycarbonate to produce a final intimate blend. Such conditions resulting in an intimate blend often include mixing in single or twin-screw type extruders or similar mixing devices well known in the art, which can apply shear to the components. It is often advantageous to apply a vacuum to the melt through at least one or more vent ports in the extruder to remove volatile impurities in the composition.
In a preferred embodiment, the concentrate is pelletized. The first polycarbonate and flame retardant salt blend is pumped in molten form through a strand die to a water bath and pelletizer. The pelletized concentrate is then further blended with a second polycarbonate.
Those of ordinary skill in the art will be able to adjust blending times and temperatures, as well as component addition, without undue additional experimentation.
The invention is further illustrated by the following non-limiting Examples.